The blast - at a chemical storage facility - jolted residents awake at 4.35am local time (10.35am BST). A series of smaller explosions followed. Flames of red and orange shot into the pre-dawn sky.
A series of smaller blasts followed, and then acrid, black smoke could be seen even in the dark. The smoke could be seen from miles away and was still rising thickly hours later as day broke.
The explosions were close to the east bank of the Mississippi River, near a residential area and rail tracks. At least two police boats were at the scene.
Chaos has spread through this desperate city since Hurricane Katrina struck, despite the promise of 1,400 National Guardsmen a day to stop the looting, a $10.5 billion recovery bill in Congress and a relief effort that President George Bush called the biggest in UShistory.
The hungry beg for help, bodies lie along flooded sidewalks, and bands of armed thugs have thwarted fitful rescue efforts.Reuse content